U.S. Pat. No. 3,902,325 of applicant refers to a mine roof support and shield structure for the face support in mines, comprising a base frame, a shield pivotally connected to said base frame and supported against this base frame by at least one prop, and at least one load-bearing rocking cap pivotally connected to said shield, noting that at least one load-bearing hinged cap is pivotally connected to said shield and that the pivotal point of the rocking cap or caps is, as seen in a top-plan view, located behind the front edge, facing the mine face, of the base frame, and noting that the pivotal point of the rocking cap, the pivotal point of the hinged cap and preferably also the point of attack of the prop or props supporting the shield structure are adjacent one another, and further noting that the shield is pivotally connected to the base frame with interposition of at least one link, the position of which link is defined by at least one strut being variable in length and acting, on the one hand, on the base frame, and, on the other hand, on the link, on the shield or on the joint connecting the link with the shield. Such a mine support and shield structure provides a good support for the mine roof and allows to support the roof of a seam by means of the hinged cap with a sufficient supporting force immediately after exposing the roof.
However, particularly with higher levels of the roof of the seam, i.e., with higher longwalls, there exists the danger that fractures occuring at the mine face will endanger the working path in the area of the longwall and persons present there, i.e., in front of the props.
The present invention aims at avoiding the mentioned deficiency of a construction according to the above-mentioned patent and essentially consists in that the prop is inclined in rearward direction and that the strut of variable length is formed of two tension links being mutually pivotally connected, the pivotal joint of that tension links being acted upon by a hydraulic cylinder-piston-means in transverse direction to said tension links, said cylinder-piston-means being supported against the base frame at the side of the tension links being opposed to the props. In view of the prop or the props being inclined in rearward direction, the lower supporting point of the prop can be advanced with the upper supporting point of the prop remaining in unchanged position. In view of this feature and in view of two mutually connected tension links being provided which are acted upon by the hydraulic cylinder-piston-means at the side opposed to the props, the space between said strut of variable length and the prop is increased such that the working path is kept free for persons staying within the longwall. This working path is now covered at its top side by the shield and by the rearward portion of the rocking cap, and is rearwardly located to such an extent that it cannot be endangered by any inroad occuring either at the mine roof or at the mine face or at the mine filling side.
In case of a rock burst, the roof of the exploitation area may suddenly sink to the lowermost position of the shield and of the cap. In view of the strut of variable length being formed of two mutually connected tension links and in view of the piston-cylinder-means acting on the connecting joint of these tension links at the side opposite to the props and in view of said piston-cylinder-means being pressure loaded, the piston is shifted into the cylinder in the case mentioned. The tension links nearly assume a stretched position, i.e., the distance between said tension links and the prop is increased. Therefore, in case of such a complete downward movement of the prop, the space between the tension links and the prop is not being narrowed but widened, so that also in such a case a sufficiently shielded operating path remains between the prop and the tension links, and accidents can be avoided. Thus, the invention provides for increased safety in mining.
According to a preferred embodiment of the invention the shield may be vaulted or kinked in outward direction and the cylinder-piston-means supporting the rocking cap against the shield can be arranged before the prop. In this manner, the free cross-section of the working path being located between the prop and the strut of variable length can be increased. By vaulting or kinking the shield in outward direction the free space is of increased height. By increasing the height of the area adjacent the supporting point of the prop and by arranging the hydraulic cylinder-piston-means before the props, this cross-section of increased height of the working path is kept free of installations.
The invention is further illustrated with reference to the drawing, which schematically shows an embodiment of a mine roof support and shield structure according to the invention.